const stream = require('stream');
var duplexStream = stream.Duplex();
duplexStream._read = function(){
    this.push('读取数据');
    this.push(null)
}
duplexStream._write = function (data, enc, next) {
    console.log(data.toString());
   next();
}
duplexStream.on('data', data => console.log(data.toString()));
duplexStream.on('end', data => console.log('读取完成'));
duplexStream.write('写入数据');
duplexStream.end();
duplexStream.on('finish',data =>console.log('写入完成'));